Staphylococcus aureus (SA) nasal carriage is a common condition that predisposes individuals to severe community-acquired and nosocomial infections, and acts as an important reservoir for spreading pathogenic strains. We are beginning to understand that host and bacterial determinants collectively contribute to the carrier state, and have utilized nasal epithelial cells and ex vivo tissue models of the upper airways to better define the role of bacterial and host determinants of SA nasal carriage. However, to confirm the in vivo role of these factors in nasal carriage, a suitable animal model of SA colonization would be required. While useful, murine models are not ideal for studying longterm SA nasal carriage or the host's response to colonization, since these animals are not naturally colonized by SA, extraordinarily high inocula result only in transient colonization, and murine noses poorly model the mucosal host response of human noses. Thus, current models do not afford the ability to test SA carriage in its natural state. Nonhuman primates would likely better serve to model human SA nasal carriage. We explored whether pigtailed macaques could be used as a biologically relevant model of experimental SA nasal colonization, and discovered that over half were nasally colonized by SA. Genetic analyses revealed sequence homology between nasal SA of humans and macaques, suggesting that pigtailed macaque noses could be experimentally colonized with human-derived SA strains. This proposal seeks to develop a tractable, cost-effective model of nasal carriage of SA in pigtailed macaques, and utilize the model to assess the host's mucosal response to SA colonization. In Aim 1, we will develop the pigtailed macaque nasal carriage model using each macaque's own SA nasal isolate, and then use the model to explore how clinically relevant nasal human SA strains colonize macaque noses. Following experimental nasal colonization with macaque and clinically relevant nasal human SA strains, level of carriage will be assessed for two months by quantifying bacterial load and genotyping the recovered SA to confirm whether colonization persists with the inoculated strains. In Aim 2, we will utilize the pigtailed macaque model to determine how nasal carriage of SA affects innate mucosal host defense in vivo. Given we have reported that nasal fluids from human carriers of SA are deficient in killing SA in vitro, we will determine whether nasal fluids from macaques that carry SA in their noses are similarly deficient before and after in vivo experimental SA colonization. We will also utilize a robust proteomic approach to evaluate the biological effect of experimental SA colonization on the expression of antimicrobial polypeptides, inflammatory markers, and other mucosal host defense components. Collectively, we would provide the field with a nonhuman primate model for studying determinants of SA nasal carriage, and testing the safety and efficacy of candidate anti-SA nasal prophylaxes.